Exam 1 Topics

Question 1

Sintering

Answer 1

atoms move by diffusion

Question 2

amorphous

Answer 2

no melting point, random molecule arrangement

Question 3

semi crystalline

Answer 3

molecules arranged in a pattern, usually have better rigidity and structural properties

Question 4

How is glass made

Answer 4

cooling so fast that there is no nucleation and no crystallization

Question 5

Surface Roughness Impacts

Answer 5

Affects wear
Lower roughness improves fatigue life

Question 6

Name NDT’s

Answer 6

Dye Penetrants
Magnaflux
Ultrasound
Radiography
Acoustic Emission

Question 7

How to increase reduction of area

Answer 7

Increase Hydrostatic pressure because triaxial tensile stresses open up voids
Improve cleanliness of material, inclusion are internal stress raisers

Question 8

When is creep a concern?

Answer 8

When the internal energy is greater than 0.5 the thermal energy required for melting.

Question 9

Remelt Ingot

Answer 9

Simple shape and composition controlled
Easy to transport and remelt

Question 10

Shape Casting

Answer 10

Cast to near final shape

Question 11

What occurs during solidification?

Answer 11

Shrinkage

Question 12

Substitutional solid solutions

Answer 12

Elements of similar size around 15%

Question 13

Interstitial Solid Solutions

Answer 13

Solute much smaller than solvent

Question 14

Eutectic

Answer 14

Two phase(Lamellar)

Question 15

What allows composition to adject with temp

Answer 15

Diffusion

Question 16

What favors grain growth

Answer 16

High temp

Question 17

what favors nucleation(fine grains result)

Answer 17

high undercooling(rapid cooling)

Question 18

Which nucleation is favored

Answer 18

Heterogeneous

Question 19

Small constitutional undercooling

Answer 19

cellular growth, small ridges formed

Question 20

Moderate constitutional undercooling

Answer 20

Dendritic growth, yields columnar grains, structure is anisotropic

Question 21

Large constitutional undercooling

Answer 21

spikes form in liquid
“Dendritic growth”
Maximizes surface Area-Volume

Question 22

Dendrites

Answer 22

Spacing not predictable
Low DeltaTc larger spacing with thicker primary dendrites
grow at constant velocity

Question 23

Very Large constitutional undercooling

Answer 23

All crystals grow dendritically, but independent nucleation starts early and no columnar zone has a chance to form. Random grains give more uniform properties

Question 24

When is high deltaTc favored

Answer 24

Large freezing temp range
Slow freezing

Question 25

What happens with shrinkage on freezing

Answer 25

fine porosity between dendrite arms, since liquid cannot readily flow between dendrites late in the freezing process

Question 26

Microsegregation

Answer 26

composition gradient through grain or dendrite Solute rich at surface

Question 27

Macrosegregation

Answer 27

composition gradients over large distances Non-uniform properties through section Non-unform response to heat treatment

Question 28

segregation

Answer 28

centers of crystals grown during nonequilibrium solidification have a different composition also known as microsegregation or coring

Question 29

what causes nonequilibrium solidification

Answer 29

cooling rates in solidification processes are fast and diffusion processes are too slow

Question 30

Surface tension

Answer 30

Effects flow Effects mold filling

Question 31

How does superheat affect fluidity

Answer 31

Increasing superheat increases fluidity and grain size

Question 32

How does mold temperature affect fluidity

Answer 32

Increased mold temp increases fluidity and grain size

Question 33

Solidification mechanism affect on fluidity

Answer 33

decreased freezing temp increases fluidity and more dendrites decreases fluidity

Question 34

What happens when grey cast iron is cast

Answer 34

It expands

Question 35

Die Casting

Answer 35

Molten metal is forced in under thousands of PSI Intricate shapes/no sand cores Primarily for non-ferrous No Risers Dendrites broken by pressure

Question 36

Ingot casting

Answer 36

continuous processing

Question 37

Name casting problems and how they originate

Answer 37

oxides and inclusions during melting during pouring from mold erosion

Question 38

Name casting problems and how they are corrected

Answer 38

deoxidize prior to pour filter/reduce turbulence sprue/gate design

Question 39

Hot tearing

Answer 39

Solidification stresses can cause a rupture of the solid network. May be brittle S/L interface or liquid

Question 40

Greater superheat...

Answer 40

means more heat must be given off during solidification, leading to slower cooling and coarser grains

Question 41

Higher superheat...

Answer 41

reduces the number of nuclei left, increasing grain size

Question 42

green sand

Answer 42

made of sand(ceramic, clay(bonding agent) and water

Question 43

Difference between green and dry sand mold

Answer 43

Green has a water content, dry is baked removing water

Question 44

Which is stronger green or dry

Answer 44

dry is stronger because there is less chance of collapsibility and the binder is strengthened

Question 45

Which mold should a hot short material be cast in

Answer 45

Hot short materials should be cast in a green sand mold because this mold allows the metal to shrink as it cools, this also reduces the stresses in the metal.

Question 46

Hot short material

Answer 46

cracking along grain boundary

Question 47

solid solutions

Answer 47

solidify over the freezing range and has a significant effect on structure. Crystals form in the direction of heat extraction but in the form of dendrites.